1. Field of the Invention
The invention relates to a process for surfacing, in particular polishing, a surface of a spectacle lens.
The invention also relates to a control-command unit, provided with a data-processing system for executing a computer program, implementing such a surfacing process, and to a surfacing machine comprising this control-command unit.
The invention also relates to a client-server communication interface for transferring a computer program implementing such a surfacing process to a remote computer and its execution on this computer, or for transferring input and output data.
Generally, the time taken to surface a surface of a spectacle lens depends on the machine used and on the material from which the surface is made.
The expression “surfacing” is understood to mean both turning machining operations, such as rough turning and/or finishing, and polishing operations.
When it is a question of polishing, the polishing time furthermore depends on the number of scans of the scanning tool over the surface of the spectacle lens, on the scanning speed and on the scanning amplitude. These parameters have an influence on the desired optical quality and the desired surface state (roughness).
The surfacing speed is not without effect on the conformity of the surface produced to the surface sought. Thus, a very low speed may ensure the conformity of a very complex surface, however it will affect the productivity thereof. In contrast, a high speed allows productivity to be increased but may affect conformity.
Furthermore, the optical function of a spectacle lens is mainly a result of two dioptres corresponding to the front and back surfaces of the spectacle lens. The topography of the surface to be produced depends on the distribution of the applied function between the front surface and the back surface of said lens. In certain cases, this distribution is such that the surface to be produced is particularly complex.
Generally, trials are carried out for complex surfaces in order to determine an optimal surfacing speed, thereby decreasing productivity.
2. Description of the Related Art
A process for machining a surface of a spectacle lens by turning is known from international patent application WO 2011/083234, in which process the rotation speed is fixed and deduced from a value representing the largest difference between mean sphere geometric values on the preset surface, and from a cylinder geometric value at a pre-determined far-vision control point.